Regular windows have frames which are generally rectangular. Shutters for such windows have been known for years. Such shutters have louvres which can be tilted between open and closed positions, for lighting or privacy.
However window openings are sometimes made with an arch shape. Typically such windows are known as fan lights. Usually, though not necessarily, such arch windows are located at the top of a doorway, but can be located anywhere depending on the design of the building.
Arch shutters, for fitting in such arch window frames are difficult to make. Clearly it is desirable that such an arch shutter shall have louvres, similar to regular shutters, and that the louvres shall be capable of being tilted between open and closed positions. Making an arch frame to match the window frame, is a first problem.
One problem is that the ends of the louvres should fit snugly against the inside of the arch frame. One solution proposed has been to secure fixed generally triangular shaped panels inside the frame. The louvres can simply abut against the vertical edges of the panels.
This is unsightly and closes off part of the arch frame so that no light can go through. If it is attempted to extend the louvres right out to the inside of the arch frame, then the curve or angle of the arch will interfere with the ends of the louvres, restrict tilting of the louvres, so that they can never be tilted fully closed. It was attempted to solve this by providing each louvre with a pivot axis located along one edge of each louvre. This was unsightly. Another problem is that the louvres must be positioned on centres which are spaced apart around the arch frame, but are spaced apart from each other by linear distances corresponding to somewhat less than the width of each louvre.
This arrangement can be difficult to achieve, in view of the fact that the arch frame, if it is an arcuate arch, curves progressively, at a greater and greater angle from the lower edge to the apex of the arch.
Another problem arises because the louvres usually made of wood, or plastic extrusion, or the like. They have an aerofoil shape in section, and have a relatively slender cross section. The ends of the louvres must receive pivot pins of some kind. Drillings for such pins must therefor be made into each end of each louvre.
However since the louvres have a slim cross section, the pins and the drillings must also be of small diameter. The pins are also received in small diameter drillings made in the side frame or arch frame. These drillings will be made diagonal to the section of the frame. In the past attempts have been made to drill such bores only from the inside of the frame. However this makes assembly of the shutter complex. Pins must somehow be inserted into the frame and the louvres, and this is difficult.
It would be preferable to drill from the outside and insert the pins right through the frame. However drills of small diameter are not suitable for drilling long holes right through the frame, diagonal to its axis. A solution must be found to this problem.